The present invention relates to centrifugal flow machines in general, and more particularly to improvements in so-called outer casings or barrel type housings for use in multistage centrifugal pumps and analogous machines.
U.S. Pat. No. 3,153,383 granted Oct. 20, 1964 to Pilarczyk discloses a multistage centrifugal pump wherein the outer casing is a one-piece body, one end portion of which is formed with an inlet opening for admission of fluid to the first stage and another end portion of which has an outlet opening for evacuation of pressurized fluid which issues from the last stage. A similar outer casing is disclosed in U.S. Pat. No. 3,051,090 granted Aug. 28, 1962 to Zumbusch. The packages of stages which are utilized in the machines of these references are held together by elongated tie bolts, and the first stage abuts against an internal shoulder of the outer casing adjacent to the inlet opening. It is also known to hold the stages of a multistage centrifugal pump together by a cover serving to close that end of the outer casing which is adjacent to the outlet opening (i.e., to the last stage) and to urge the foremost stage against an internal shoulder of the outer casing. Thus, the shoulder serves to take up all forces which develop in the interior of the outer casing and are determined by the pressure of fluid in the machine as well as by the configuration and dimensions of the parts in the outer casing. It can be said that the plane including the internal shoulder of a conventional outer casing constitutes a partition between the low-pressure region which receives fluid from the inlet opening and the high-pressure region which admits pressurized fluid to the outlet opening. In order to ensure that the shoulder will be capable of standing the stresses which develop in the interior of the outer casing, the material around the shoulder must exhibit a certain thickness. Moreover, the shoulder determines the inner diameter of the outer casing. Therefore, the portion of the outer casing in the region of the inlet opening is normally much thicker than the portion which is adjacent to and defines the outlet opening even though the pressure at the outlet opening is much higher than the pressure at the inlet opening. The pressure at the outlet opening depends on the number of stages and on the design of stages in the outer casing. The making of a one-piece outer casing involves considerable waste in expensive metallic material and resort to complex material removing machines. Moreover, the outer casing is often too bulky and too heavy, and the assembly of the component parts therein by means of tie bolts takes up much time.